Dispersal and colonization are stochastic processes that can impact assembly of ecological communities. In addition, colonization order, often referred to as priority affects, can leave a lasting impact on community composition through time. In the case of host-associated microbial communities, the presence of priority effects has applied implications for the administration of probiotics to a target host organism. The global prevalence of the amphibian fungal pathogen, Batrachochytrium dendrobatidis, and the potential of host-associated skin bacteria to mitigate the effects of this pathogen, have made probiotic treatments of high interest in the field of amphibian conservation. We sought to determine if priority effects impact bacterial community assembly on newly-hatched tadpoles. To answer this question, we selectively inoculated the eggs of lab-raised hourglass tree frogs, Dendropsophus ebraccatus, over two days with two bacterial taxa (Genera: Acinetobacter and Stenotrophomonas) isolated from the skin of wild adult frogs. On day one, each egg received an inoculation of one of our chosen isolates or sterile water. On the second day, eggs received either the same isolate, the alternate isolate, or sterile water. By altering the order in which isolates were received we hoped to elucidate the impact of priority effects on tadpole bacterial communities. The effect of the treatments on the tadpole bacterial microbiome was assessed after hatching using 16S rRNA gene sequencing.
Results/Conclusions
We found significant differences in bacterial community composition on newly-hatched tadpoles based on our treatment groups. Changing the order in which eggs were inoculated with our two selected bacterial isolates led to changes in both the relative abundances of bacterial taxa and in the presence or absence of specific taxa. Still, tadpoles developed a diverse bacterial symbiont community even when treated with bacterial isolates: bacterial species richness, phylogenetic diversity, and the effective number of species on the tadpoles were not strongly impacted by colonization order. Overall, these results support priority effects playing a role in the initial assembly of the amphibian microbiome, especially by impacting community structure.